This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from applications for ELECTRON GUN FOR CATHODE RAY TUBE earlier filed in the Korean Industrial Property Office on Oct. 15, 2001 and there duly assigned Serial No. 2001-63448, for ELECTRON GUN FOR CATHODE RAY TUBE earlier filed in the Korean Industrial Property Office on Oct. 17, 2001 and there duly assigned Serial No. 2001-64092, for ELECTRON GUN FOR CATHODE RAY TUBE filed in the Korean Industrial Property Office on Oct. 17, 2001 and there duly assigned Serial No. 2001-64093, and for ELECTRON GUN FOR CATHODE RAY TUBE earlier filed in the Korean Industrial Property Office on Apr. 10, 2002 and there duly assigned Serial No. 2002-19558.
1. Technical Field
The present invention relates to an electron gun for a cathode ray tube. More particularly, the present invention relates to an electron gun that may be applied to a cathode ray tube which requires electron beams of an extremely minute (small) spot size.
2. Related Art
In general, a cathode ray tube needs an electron gun capable of optimizing the diameter of an electron beam spot striking against a phosphor screen for improving a resolution characteristic.
For example, in the beam index cathode ray tube (CRT), which is one type of CRT, since color images are realized without the use of a shadow mask that performs color separation of the electron beams as in conventional CRTs, it is necessary in the beam index CRT for the electron gun to emit electron beams having a cross section that is within specific dimensional limits. That is, with reference to FIG. 38, so that an electron beam E/B landing on a phosphor screen 1 selectively illuminates only a desired phosphor layer 3, it is necessary that a spot formed by the landing of the electron beam E/B is substantially elliptical with a vertical major axis (i.e., major axis corresponding to the Y axis in the drawing) and a minor axis (in an X axis direction in the drawing) of a minimal length. In particular, a minor axis length (r) of the electron beam spot must be smaller than the sum of a width w1 of one phosphor layer 3 and widths w2 of black matrix regions 5 on both sides of the same phosphor layer 3 to prevent the landing of the electron beam E/B on a phosphor layer 7 of a different color.
Therefore, when compared to conventional CRTs that use a shadow mask, the beam index CRT must realize a beam diameter in the horizontal direction of the phosphor screen that is as small as possible.
Japanese Laid-Open Patent No. Sho 53-76737 by Shimoma discloses an electron gun having a first grid electrode with an elliptical aperture having a vertical major axis and a second grid electrode with an elliptical aperture having a horizontal major axis. Further, Japanese Laid-Open Patent No. Heisei 6-203766 by Yanai discloses an electron gun used in a color image receiving tube, in which apertures formed in first and second grid electrodes are elliptical with a vertical major axis and having a ratio of the major axis to the minor axis of 1.2xcx9c4.5.
In addition, Japanese Laid-open Patent No. Heisei 8-212947 by Iguchi et al. discloses an electron gun, in which a pair of electromagnetic quadruple poles and/or electrostatic quadruple poles are formed in a main focus lens region at a location where the main lens is formed or in a direction toward a cathode with respect to the main lens. Also, Japanese Laid-Open Patent No. Heisei 9-259797 by Iguchi et al. discloses an electron gun in which a trajectory of electron beams is controlled by an octuple pole electron lens means.
In the above configurations, by improving electron beam apertures formed in the first and second grid electrodes or by installing quadruple or octuple poles that influence the trace of electron beams, electron beam spots of an elliptical shape with a vertical major axis are realized at the center of the screen, and focus characteristics are improved by rotating the electron beams at circumferential areas of the screen.
However, with the use of the above electron guns, a structure to interconnect a focus electrode and an anode electrode, which form a main lens, is such that the spot size of the electron beam landing on the phosphor screen is increased (i.e., the minor axis of the elliptical electron beam spot, which has a vertical major axis, is increased) in the case where a cathode current is increased to realize bright pictures such as a snowy scene or a picture that displays characters on a white background. Spherical aberration caused as a result increases the spot size of the electron beams landing on the phosphor screen. If such electron beams are used in a beam index CRT, unintended phosphor layers of different colors are illuminated by the increased spot size of the electron beams such that picture quality significantly deteriorates.
U.S. Pat. No. 4,271,374 for Electron Gun for Cathode-ray Tube by Kimura discloses an electron gun, in which part of the focus electrode, in particular, a final focus electrode opposing an anode electrode is positioned within the anode electrode such that an aperture of a main lens is optimized. Therefore, spherical aberration initiated in the main lens is decreased to thereby minimize the spot size of the electron beams landing on the phosphor screen.
However, with the overlapping of the final focus electrode and the anode electrode in this electron gun, the aperture of the main lens formed between the final focus electrode and the anode electrode is enlarged such that while a small beam diameter may be realized, the structure of electrodes forming the main lens is complicated and difficult to manufacture. Also, because of this overlapping structure of the electrodes, internal voltage characteristics deteriorate such that a voltage difference between the final focus electrodes and the anode electrode cannot be increased.
In addition, with the overlapping structure of the final focus electrode and the anode electrode, in the case where a frequency of a deflection device is increased or a separate secondary coil is mounted to an external circumference of the panel or neck between the electron gun and deflection device to control focus characteristics and a deflection linearity of the electron beams, eddy currents are generated where the electrodes overlap. As a result, a control sensitivity of the electron beams is decreased.
It is therefore an object of the present invention to provide an electron gun for a cathode ray tube, in which a spot size of electron beams in a horizontal direction of a phosphor screen is minimized while simplifying a structure of electrodes forming a main lens.
It is another object to provide an electron gun that is suitable for use in a beam index cathode-ray tube.
It is yet another object to provide an easy and inexpensive design and manufacture of an electron gun with a simple structure of the final focus electrode and the anode electrode, which form the main lens.
It is still another object to provide an electron gun which prevents eddy currents from generating between the final focus electrode and the anode electrode and therefore reducing the focusing characteristics caused by the eddy currents during operation.
To achieve the above and other objects, the present invention provides an electron gun for a cathode ray tube, the electron gun including a single cathode that emits thermions; first and second electrodes forming a triode structure with the cathode; a plurality of focus electrodes provided consecutively after the second electrode in a direction away from the cathode; an anode electrode mounted after a final focus electrode, which is farthest from the cathode among the focus electrodes; and a support that supports the electrodes in an aligned configuration.
The final focus electrode and the anode electrode are mounted opposing one another with a predetermined gap therebetween, and if a lengthwise direction of phosphor layers forming a phosphor screen of the cathode ray tube is referred to as a Y axis direction, and a direction perpendicular to the Y axis direction is referred to as an X axis direction, an electron beam aperture formed in a portion of the final focus electrode opposing the anode electrode, and an electron beam aperture formed in an area of the anode electrode opposing the final focus electrode have diameters in the X axis direction that are larger than diameters in the X axis direction of electron beam apertures formed in the electrodes between the cathode and the final focus electrode.
The electron beam aperture formed in the portion of the final focus electrode opposing the anode electrode, and the electron beam aperture formed in the area of the anode electrode opposing the final focus electrode have diameters in the X axis and Y axis directions that are larger than diameters in the X axis and Y axis directions of the electron beam apertures formed in the electrodes between the cathode and the final focus electrode.
The electron gun further includes an intermediate electrode mounted between the final focus electrode and the anode electrode with a predetermined gap between the intermediate electrode and the final focus electrode and between the intermediate electrode and the anode electrode, the intermediate electrode receiving a voltage that is greater than a voltage applied to the final focus electrode and less than a voltage applied to the anode electrode.
A diameter of an electron beam aperture formed in the intermediate electrode is larger than the diameters of the electron beam apertures formed in the electrodes between the cathode and the final focus electrode.
The voltage is applied to the intermediate electrode through a resistive member, which is mounted along a length of one side of the support and connected to the intermediate electrode and the anode electrode.
The electron gun further includes a shield cup having a main surface through which an electron beam aperture is formed, the main surface contacting the anode electrode; and a plate electrode assembly having a pair of plate electrodes that are formed at a predetermined spacing on the main surface with the electron beam aperture provided between the plate electrodes, the plate electrodes extending into the anode electrode.
The electron beam aperture formed in the first electrode is elliptical with a major axis in the Y axis direction, the electron beam aperture formed in the second electrodes is quadrilateral, and a slot is formed in a surface of the second electrode facing the focus electrodes, the slot being formed lengthwise in the X axis direction.